Glen Hewlett has managed to convert Space Invaders from the original Intel 8080 Arcade source code to the Motorola 6809 that runs on the CoCo 3.

He starts the article explaining that since he never understood Interrupts back in the 80’s, he decided to try to write something for the CoCo to practice some of the information he learned from John Linville in his CoCo Crew Podcast Tech Talk.

Instead of writing something from scratch, Glen decided to write a port of a famous arcade game:

I started looking into the hardware of Pac Man and I found pretty quickly that it has some hardware the CoCo doesn’t namely sprites for graphics. Since I don’t know much about computer sprites I decided to start my transcoding to an older more simpler game that would be a good starting point to get my 6809 programming skills back in order. So I decided Space Invaders would be a great game to start with.

To help the translation he wrote a C program for the task, which he has made available with the Space Invaders port on TRS-80 Color Computer Archive website, and we are also making it available here on Vintage is The New Old (link below).

Running the port is pretty easy using MESS emulator with any coco3 ROM installed. You use 5 to “insert the coin”, 1 or 2 to select the number of players, <space> to shoot and arrows to move the cannon. When you fist start the game, you will see it plays sideways, which is expected since that is the way the arcade CRT was mounted. MESS allows you to rotate the screen, so it looks “correct, ” and you can play it just fine!

I talked to Glen via email as I was writing this and he told me that the Space Invaders port took about one month and a half to be completed and his next project is to translate Pac Man code for the 6809. We can’t wait to see this new one!

He finishes saying that the ZIP containing the port and his C utility is freely available and he hopes more people learn from it.

To read all the tech details of the task, head over Glen’s blog, following the link below.